Three-lens system for photographic purposes.



No. 635,473. Patented Oct. 24, 1899. C. P. GOEBZ &. E. VON HUEGH.

THREE LENS SYSTEM FOR PHOTOGRAPHS PURPOSES.

(Application filed In. 1, 1899.)

(No Model.)

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flllanzey.

UNITED STATES PATENT OFFICE.

CARL PAUL GOERZ AND EMIL VON HOEGH, OF FRIEDENAU, GERMANY.

THREE-LENS SYSTEM FOR PHOTOGRAPHiC PURPOSES.

SPECIFICATION forming part-0f Letters Patent No. 635,473, dated October24 1899.

Application filed March 1, 1899.

.15 by a layer of air having the form of a positive meniscus.

In the accompanying drawings, Figures 1 and 2 represent axial sectionsthrough two possible forms of the new composite lens.

In the present three-lens systems there is a lens of average refractivepower inclosed between two other lenses, one of which-is of smaller, theother one of higher, refractive power. The useful aperture of suchcompos ite systems and the intensity of the luminous rays passing itdepend upon the value of the difference between the refractive indicesof two neighboring lenses. The smaller this difference the smaller isalso to be the radius of the curvature of the surface of the lens. Ifthis were not the case, the elimination of the spheric and astigmaticaberration would not be possible. It is evident that there exists acertain minimum for the curvature which cannot be passedwithoutimpairing the sharpness of the images produced. The differentkinds of glass preferably employed in the construction of such lenseshave refractive indices between 1.51 and 1.61. It was men-. tionedbefore that the inclosed lens is to have a refractive index betweenthose of the two other lenses. Consequently the differences of theindices of refraction between the central lens and the neighboring onescannot possibly exceed the value of 0.05.

In order to obtain a greater power for concentrating the light withoutaugmenting the number of the lenses composing the system and eliminatingat the same time all errors 50 and obtaining a very sharp image, we donot employ the cemented surface acting as a disperser, as hereinbeforedescribed, but employ Serial No. 707,420. (No model.)

different radii for the curvature of the surfaces forming thecollecting-surface S. lVe make the radius of the surface of the negative lens shorter than the one belonging to the neighboring surface ofthe positive lens, thereby leaving between the two lenses an air-spacehaving the form of a positive me niscus. The consequence of thisarrangement is that for compensating the spherical aberration we need nonegative lens of higher refractive power than the positive one, or, inother words, that the glass of which the inclosed lens is formed has tobe of refractive power the value of which lies between the correspondingvalues of the two other lenses. If the inclosed lens is, as shown inFig. 1, a biconcave (negative) one, it may consist of material havingvery low refractive power. On the other hand, if the middle lens is abiconvex (positive) one the glass may be of the highest possiblerefractive index. In both cases the direct consequence is that two kindsof glass having a very great difierence of the refractive indices arecemented together at the collectingsurface S, and itis obvious that theelimination of the astigmatic aberration is attained with a considerablygreater radius of curvature of the surface of the lens.

Another important advantage resulting from the hereinbefore-describedarrangement is that the new composite objective gives sharper images andhas higher illuminating power. Furthermore, this arrangement allows thestrict fulfilment of the so-called sine condition.

The numbers inscribed in the drawings signify the value of therefractive indices of the glass employed preferably for the manufactureof the respective lenses.

S is the cemented surface of the inclosed lens, which acts as acollector, whereas Z is the second one, acting as a disperser.

It is evident that two of the described threelens systems may be unitedwith each other to form a composite objective for photographic purposes.

What we claim is 1. In a three-lens system for photographic purposes thecombination with a lens, formed by cementing together a biconvex lens ofhigh-refractive index and a biconcave lens of low-refractive index, of ameniscus the surbiconcave lens having a longer radius, than the oppositesurface of the biconoave lens, V substantially as shown and described.

In testimony whereof we affix our signa- 15 tures in presence of twowitnesses.

CARL PAUL eoERz. EMIL voN HOEGH.

Witnesses:

HENRY HASPER, WOLDEMAR HAUPT.

